This invention relates to radar signal processing circuits and in particular to a balanced input zero differential detector for determining the centroid of the video pulse of a returned echo.
In modern radar signal processing it is of interest to determine the "center of gravity" or centroid of the video pulse of a returned echo. A recognized practice is to use the following concept. First, the linear pulse signal with noise is amplified on a log-amplifier, which gives an output pulse with "cleaner" signal near the center. This compressed signal is fed to a terminated delay line along which a number of equally spaced taps are provided. Four taps, for example, may be utilized. The sum of the first group of taps is then compared with the sum of the second group of taps. Generally the difference between the first group and second group is shown as a curve in which the zero crossing represents the centroid of the incident pulse. A zero crossing detector is used to determine the point. Specifically, the task of the zero crossing detector is to determine a crossing "0" as precisely and as fast as possible without responding to the noise on the skirts of the pulse.
The zero crossing detector must have high time precision, high amplitude sensitivity and dynamic range, very fast response time and be insensitive to base line noise perturbations. It should also be able to reset itself automatically to enable proper response to multiple incoming signal pulses or echoes. The present invention is directed toward providing a differential detector that satisfies these requirements.